The present invention provides a method and apparatus for testing vehicle fuel system integrity and, in particular, to testing the vehicle fuel system with combustible fuel in the fuel system tank. The invention obtains a leakage parameter, such as size of the leak opening, leak rate, or the like.
The ability to detect the proper functioning of a vehicle's fuel tank system is necessary for controlling the emissions of VOCs into the environment. EPA issued a procedure for determining the pass/fail status of a vehicle's fuel tank integrity, but did not take into account the variation in results due to different vapor space volumes.
A real vehicle with fuel is subject to a contribution of mass from the evaporation of fuel in the tank. This contribution affects the system by replacing mass lost to a leak and, thus, masking the ability to detect a leak. It is well known in the field that this may theoretically be compensated for by characterizing the vapor pressure of various fuels at various temperatures. However, the fuel blend is not usually known, is effected by age, and the rate of vapor contribution is effected by the geometry of the system, which may also not be known. Thus, this effect was generally not taken into account in known procedures.